Syrian soldiers and security forces approach people who have met UN truce mediators after they leave a town and sometimes those people may be killed, mediator Kofi Annan's spokesman Ahmad Fawzi said on Tuesday, citing what he called credible reports.

Fawzi, in remarks on UN Television, also said satellite imagery showed that Syrian forces had not withdrawn heavy weapons from urban centers and returned to their barracks, as they are required to do under the Annan plan.

"They (Syrian authorities) are claiming that this has happened. Satellite imagery, however, and credible reports show that this has not fully happened, so this is unacceptable, and Joint Special Envoy Kofi Annan will be saying this to the Security Council today when he addresses them in closed session," Fawzi said.

A car bomb wounded at least three people earlier on Tuesday near Yelbagha complex in the central district of al-Marjeh in Damascus, the pro-government Syrian television channel (SANA) said. Reuters reported that the explosion was near an Iranian cultural center.

The SANA television channel blamed "armed terrorists."

A SANA reporter quoted a source in the Damascus Police that the explosive device was placed under a car. One of the injured in the explosion was the car driver.

In a separate incident near Damascus, SANA and opposition sources reported that an intelligence officer, Lieutenant Colonel As'aad Ahmad Ismael and his brother in Jedaydet al-Fadel, were killed.

Previously, the Syrian army had killed more than 20 people in Hama on Monday, activists said, shattering a week of relative quiet in the central city visited a day earlier by UN monitors laying the ground for a wider mission to oversee a shaky 11-day ceasefire.

A small group of unarmed observers has been in Syria for a week, tracking the truce between forces loyal to Syrian President Bashar Assad and opponents inspired by 'Arab Spring' uprisings in North Africa and elsewhere in the Middle East.

The deal has curbed some of the violence, but the latest killings in Hama's Arbaeen district have laid bare the difficulty of bringing to a complete halt 13 months of fighting in which more than 9,000 people have died.

The UN Security Council has approved an expansion of the monitoring mission to 300 observers, although Assad's opponents say such numbers are far too small to keep a track on events in a nation of 23 million.Jpost.com staff contributed to this story.